Tol. 67.] SKOMER VOLCANIC SERIES. 205 



XIII. XIV. XV. 



Si0 2 53-82 5268 52-13 



Ti0 2 166 ... notdt. 



Al.,0, 14-70 1414 14-87 



Fe 2 3 239 195 nut det. 



FeO 674 9-79 11-10 



MnO 039 0-44 0"32 



(CoNi)O '. 003 n.d. 



BaO 002 n.d. 



CaO 9-03 9-38 10-50 



MgO 4-84 6-38 6*46 



K.,0 1-85 0-87 069 



Na,0 2-75 2*56 2-60 



Li.,0 notfd. 



H;Oatl05°C 0-371 ^^ 1>ig 



H,0 above 105° C. ... 159 J 1 <)U l iy 



P.O. 0-10 ... notdet. 



C0 2 010 



Totals 100-38 99-79 100-22 



Anal E. G-. Iladley. G. W. Hawes. A. Streng. 



XIII = Granulitic basalt (lava); above tbe Limekiln (Skonier). [Analysis 



Xo. 344. Slide E 7766.] 

 XIV=Dolerite (diabase) ; Mount Holyoke, Mass. (U.S.A.). G. W. Hawes, 

 Amer. Journ. Sci. ser. 3, vol. ix (1875) p. 186. 

 XV = 'Trap '; Giants' Causeway (Antrim). Pogg. Ann. vol. xc (1853) p. 114. 



rock of which the analysis is tabulated above would be designated 

 auvergnose (Symbol III, 5.1.3), and would take its place 

 among a series of extrusive and intrusive rocks, of which the dolerite 

 of Mount Holyoke approximates most closely to it in chemical 

 composition (Analysis XIV) ; while certain rocks at the Giants' 

 Causeway, Antrim, resemble it in many respects (Analysis XV). 



A striking difference between the Skomer rocks and many of 

 the Tertiary flows of other regions is the complete absence of 

 zeolitization, for no zeolites have as yet been detected infilling 

 the vesicles of Skomer basaltic rocks. The cavities are always 

 filled with what would be regarded as the normal products of 

 weathering, such as chlorite, epidote, etc. 



{h) The Olivine-Dolerites. 



These rocks are not of very frequent occurrence, but are of wide 

 vertical and horizontal distribution. They occur at the southern 

 end of the Smalls; on Skomer in Pigstone Bay above the sediments, 

 and in the cliffs above the Table, in South Haven above the sedi- 

 ments, and associated with sediments at the bottom of Matthew's 

 Wick ; on the mainland at Hopgang. 



They exist as masses of much greater thickness (20 feet) than is 

 usual for the flows ; while microscopically they present all the 

 appearances of intrusive rocks, with the exception of chilled 

 margins. 



In the hand-specimens they are more compact and less vesicular 



